In a charged particle beam device, such as a scanning electron microscope, a transmission electron microscope, an ion microscope, and a semiconductor inspection device, a sample is irradiated with charged particle beams generated under a high vacuum environment, and an observation image of the sample is acquired by detecting electrons reflected at the sample, electrons passing through the sample, secondary electrons emitted from the sample, or the like.
There is a scanning electron microscope (SEM) as a representative example of the charged particle beam device. The scanning electron microscope includes an electron gun formed of an electron source of a field emission type or a thermal field emission type, and electron beams emitted from the electron gun are accelerated and made into thin electron beams at an electron lens. In the scanning electron microscope, the sample is scanned with the electron beams as primary electron beams by using a scan deflector, and an image is acquired by detecting obtained secondary electrons or reflected electrons. As a material of the electron source, tungsten is used in the case of a general-purpose SEM. Further, as a material of the electron source used for semiconductor observation, zirconia may be contained in tungsten.
In order to emit good electron beams from the electron source for a long period, the vicinity of the electron source is needed to be kept in a high vacuum state (10−7 to 10−8 Pa). Therefore, in the related art, there is a method of forcedly evacuating air in the vicinity of the electron gun with an ion pump. Further, there is a charged particle beam device in which a higher vacuum state is obtained by including a non-evaporable getter pump (PTL 1, for example).